It is known to provide electronic processors with a central memory and a mass memory, allowing programs to be carried out only if they are recorded in the central memory. Besides, while in the mass memory programs are recorded in a permanent way, in the central memory they may be missing or be destroyed for many reasons. For instance, programs must be introduced into the central memory when a computing system is used for the first time; if the memory is made of semiconductors, it must be loaded again every time after the processor has been cut off. If the memory is of a different structure, consisting, for instance of magnetic cores, the memory is to be loaded again after a stop occurred because of an error or a failure.
Transfer of main programs from the mass memory to the central memory is controlled by an instruction sent to the mass memory by the processing devices; yet this instruction is in turn an ancillary program (named "bootstrap" in the art) that the central memory shall send to the processing devices. This "bootstrap" program comprises, besides the actual transfer command, also the check of the final correctness of the transferred information. It is consequently a rather complex program and cannot be loaded manually into the central memory, but must be permanently recorded somewhere, for instance in a read-only memory.
This read-only memory in some very sophisticated processors is directly inserted into the computing system and its controlled by a pushbutton placed on the console.
The unquestionable operative advantage offered by such a solution is counterbalanced by the fact that the "bootstrap" must be dealt with in the overall design of the computing unit, aside from the problem that the computing unit itself is encumbered by a device which can be useful only in some cases. In some processors of a different kind the "bootstrap" is added to the central memory. This entails an encumbrance and greater costs for the central memory, as in the "bootstrap" some functions may exist which are not necessary to the transfer to be carried out and which lenghten the program. Besides, the type of encoding by which this ancillary program is recorded is generally, not a natural coding, that is it does not allow the optimum utilization of the processor code (for instance the use of sub-routines).
In the more usual processors, on the other hand the "bootstrap" is recorded in an external unit which can be either a tape or a card and it must be transferred into the central memory in order to be implemented by the processor.
There are some types of processors in which such a transfer operation from the external unit is controlled by a special circuit inserted in the operative unit of the processor. In other types of processors this circuit does not exist; in these cases it is necessary to prerecord a short program for loading into the central memory the contents of the external unit and make it operational. Recording of this program is generally carried out manually by means of suitable control devices placed on the console of the operative unit. Yet possible errors may affect these operations, and the need arises that the program be as short as possible; but if it is too short, it means that it does not sufficiently control the operation of transfer from the external unit to the loading area. Also, the external unit generally contains a relatively short program in which there are no particular checking operations and redundancies. These circumstances may cause errors which will be detected only when the "bootstrap" becomes operative, entailing disadvantages which are well known to the skilled in the art.